42 ] 
RECORDS OF W.A. MUSEUM. 
The rest of the tooth consists of two ridges at right angles united 
in front and enclosing a simple valley behind. The outer ridge 
occupies about two-thirds of that side of the tooth and contains an 
anterior tubercle, the enamel of which is partly worn away, 
exposing a ridge-shaped surface of dentine having its apex 
posteriorly. The interior angle of the tooth is occupied by a 
tubercle which, too, is so worn as to expose the dentine; in this 
instance also triangular, but with the base situated intero-posteriorly 
and covering a much larger area than the other two patches already 
referred to. The surface of this patch is much lower than the 
others and slopes so that the base is considerably lower than the 
apex of the triangle. There is a slight swelling at the base of the 
posterior aspect which may represent a rudimentary cusp or 
tubercle. 
The anterior tubercle is divided from the posterior crown by 
two valleys, each falling from a slight bridge which connects this 
cusp with the rest of the tooth and each closed by a slight ridge. 
The valley enclosed by the two posterior ridges slopes very 
abruptly to the posterior margin of the tooth, where it also was 
enclosed by a confining cingulum or ridge which has its origin at 
the base of the anterior tubercle of the longitudinal ridge ; it runs 
along the base of the exterior, and at the extero-posterior angle 
rises half way up to the summit of the tooth, then it again descends 
to enclose the posterior valley, and appears to ascend to the present 
worn surface of the internal tubercle. It can then be traced down 
the anterior face, across the mouth of the antero-internal valley and 
into the mass of tubercle of the anterior talon. 
The fangs are typical of Dipvotoiion and Nototherium premolars. 
The premolars of Dipyotodon and Nototherium have led to a great 
amount of confusion. Phe milk teeth have been mistaken for 
permanent ones, and teeth of the one genus have been ascribed to 
animals of the other. The upper premolar (D3 of Owen) of 
Dipyotodon is not often found in the jaw as, being deciduous, it is 
shed as the animal approaches maturity. Prof. Owen figures a 
tooth from the lower jaw^ m its natural position taken from a 
sketch transmitted to him by a Dr. E. A. Hobson— which shows 
r Ext. Mamm. Australia, p. 204, 1877 
